Thermoplastic fastener products having an array of integrally formed, upstanding, engageable fastener elements are employed in a wide variety of instances to enable releasable attachment of two surfaces. Often such products are formed in discrete mold cavities by injection molding techniques. Some such fastener products are said to be "self-engaging", that is, capable of engaging an identical product to form a fastening. Some self-engaging fastener elements are called "mushroom-shaped" because they have stems with overhanging heads. Because of their widespread commercial use, more efficient and cost-effective methods and machines for producing these fastener products are desirable.